The present invention generally relates to materials useful as components of cytotoxic therapeutic agents. More particularly, the invention relates to ribosome-inactivating proteins, to analogs of ribosome-inactivating proteins, to polynucleotides encoding such proteins and analogs, some of which are specifically modified for conjugation to targeting molecules, and to gene fusions of polynucleotides encoding ribosome-inactivating proteins to polynucleotides encoding targeting molecules.
Ribosome-inactivating proteins (RIPs) comprise a class of proteins which is ubiquitous in higher plants. However, such proteins have also been isolated from bacteria. RIPs are potent inhibitors of eukaryotic protein synthesis. The N-glycosidic bond of a specific adenine base is hydrolytically cleaved by RIPs in a highly conserved loop region of the 28S rRNA of eukaryotic ribosomes thereby inactivating translation.
Plant RIPs have been divided into two types. Stirpe et al., FEBS Lett., 195(1,2):1-8 (1986). Type I proteins each consist of a single peptide chain having ribosome-inactivating activity, while Type II proteins each consist of an A-chain, essentially equivalent to a Type I protein, disulfide-linked to a B-chain having cell-binding properties. Gelonin, dodecandrin, tricosanthin, tricokirin, bryodin, Mirabilis antiviral protein (MAP), barley ribosome-inactivating protein (BRIP), pokeweed antiviral proteins (PAPs), saporins, luffins, and momordins are examples of Type I RIPs; whereas Ricin and abrin are examples of Type II RIPs.
Amino acid sequence information is reported for various ribosome-inactivating proteins. It appears that at least the tertiary structure of RIP active sites is conserved among Type I RIPs, bacterial RIPs, and A-chains of Type II RIPs. In many cases, primary structure homology is also found. Ready et al., J. Biol. Chem., 259(24):15252-15256 (1984) and other reports suggest that the two types of RIPs are evolutionarily related.
Type I plane ribosome-inactivating proteins may be particularly suited for use as components of cytotoxic therapeutic agents. A RIP may be conjugated to a targeting agent which will deliver the RIP to a particular cell type in vivo in order to selectively kill those cells. Typically, the targeting agent (e.g., an antibody) is linked to the toxin by a disulfide bond which is reduced in vivo allowing the protein toxin to separate from the delivery antibody and become active intracellularly. Another strategy for producing targeted cytotoxic proteins is to express a gene encoding a cytotoxic protein fused to a gene encoding a targeting moiety. The resulting protein product is composed of one or more polypeptides containing the cytotoxic protein linked to, for example, at least one chain of an antibody.
A variety of such gene fusions are discussed in Pastan et al., Science, 254:1173-1177 (1991). However, these fusion proteins have been constructed with sequences from diphtheria toxin or Pseudomonas aeruginosa exotoxin A, both of which are ADP-ribosyltransferases of bacterial origin. These protein toxins are reported to intoxicate cells and inhibit protein synthesis by mechanisms which differ from those of the RIPs. Moreover, diphtheria toxin and exotoxin A are structurally different from, and show little amino acid sequence similarity with, RIPs. In general, fusion proteins made with diphtheria toxin or exotoxin A have been immunogenic and toxic in animals, and are produced intracellularly in relatively low yield. Another strategy for producing a cytotoxic agent is to express a gene encoding a RIP fused to a gene encoding a targeting moiety. The resulting protein product is a single polypeptide containing a RIP linked to, for example, at least one chain of an antibody.
Because some RIPs, such as the Type I RIP gelonin, are primarily available from scarce plant materials, it is desirable to clone the genes encoding the RIPs to enable recombinant production of the proteins. It is also desirable to develop analogs of the natural proteins which may be easily conjugated to targeting molecules while retaining their natural biological activity because most Type I RIPs have no natural sites (i.e. available cysteine residues) for conjugation to targeting agents. Alternatively, it is desirable to develop gene fusion products including Type I RIPs as a toxic moiety and antibody substances as a targeting moiety.
The present invention also provides novel humanized or human-engineered antibodies and methods for producing such antibodies which may be conjugated or fused to various toxins. Such conjugations or fusions are useful in the treatment of various disease states, including autoimmune diseases and cancer.
There are several reports relating to replacement of amino acids in a mouse antibody with amino acids normally occurring at the analogous position in the human form of the antibody. See, e.g., Junghaus, et al., Cancer Res., 50: 1495-1502 (1990) and other publications which describe genetically-engineered mouse/human chimeric antibodies. Also by genetic engineering techniques, the genetic information from murine hypervariable complementarity determining regions (hereinafter referred to as xe2x80x9cCDRsxe2x80x9d) may be inserted in place of the DNA encoding the CDRs of a human monoclonal antibody to generate a construct encoding a human antibody with murine CDRs. See, e.g., Jones, et al., Nature, 321: 522-525 (1986).
Protein structure analysis on such xe2x80x9cCDR-graftedxe2x80x9d antibodies may be used to xe2x80x9cadd backxe2x80x9d murine residues in order to restore lost antigen-binding capability, as described in Queen, et al, Proc. Natl. Acad. Sci. (USA), 86:10029-10033 (1989); Co, et al., Proc. Nat. Acad. Sci. (USA), 88: 2869-2873 (1991). However, a frequent result of CDR-grafting is that the specific binding acitvity of the resulting humanized antibodies may be diminished or completely abolished.
As demonstrated by the foregoing, there exists a need in the art for cloned genes encoding Type I RIPs, for analogs of Type I RIPs which may be easily conjugated to targeting molecules, and for gene fusion products comprising Type I RIPs, and especially wherein such gene fusions also comprise an humanized antibody portion.
The present invention provides purified and isolated polynucleotides encoding Type I RIPs, Type I RIPs having a cysteine available for disulfide bonding to targeting molecules and fusion products comprising Type I RIPs. Vectors comprising the polynucleotides and host cells transformed with the vectors are also provided.
A purified and isolated polynucleotide encoding natural sequence gelonin (SEQ ID NO: 11), and a host cell including a vector encoding gelonin of the type deposited as ATCC Accession No. 68721 are provided. Further provided are a purified and isolated polynucleotide encoding natural sequence barley ribosome-inactivating protein and a purified and isolated polynucleotide encoding momordin II.
Some of the polynucleotides mentioned above encode fusion proteins of the present invention comprising gelonin (SEQ ID NO: 2) or another RIP and an antibody or a fragment comprising an antigen-binding portion thereof. Several alternate forms of fusion proteins comprising gelonin are contemplated herein. For example, the fusion protein may contain a single RIP fused to a monovalent antibody binding moiety, such as a Fab or single chain antibody. Alternatively, multivalent forms of the fusion proteins may be made and may have greater activity than the monovalent forms. In preferred embodiments of the invention, gelonin may be fused to either the carboxy or the amino terminus of the antibody or antigen-binding portion of thereof. Also in a preferred embodiment of the invention, the antibody or fragment thereof comprising an antigen-binding portion may be an he3 antibody, an he3-Fab, an he3 Fd, single-chain antibody, or an he3 kappa fragment. The antibody or antigen-binding portion thereof may be fused to gelonin by means of a linker peptide, preferably a peptide segment of shiga-like toxin as shown in SEQ ID NO: 56 or a peptide segment of Rabbit muscle aldolase as shown in SEQ ID NO: 57 or a human muscle aldolase, an example of which is reported in Izzo, et al., Eur. J. Biochem, 174: 569-578 (1988), incorporated by reference herein.
Analogs of a Type I plant RIP are defined herein as non-naturally occurring polypeptides that share the ribosome-inactivating activity of the natural protein but that differ in amino acid sequence from the natural type I RIP protein in some degree but less than they differ from the amino acid sequences of other Type I plant RIP. Preferred analogs according to the present invention are analogs of Type I plant RIPs each having a cysteine available for disulfide bonding located at a position in its amino acid sequence from the position corresponding to position 251 in SEQ ID NO: 1 to the carboxyl terminal position of the analog. SEQ ID NO: 1 represents the amino acid sequence of ricin A-chain. Other preferred analogs according to the invention are Type I RIPs each having a cysteine available for disulfide bonding at a position in the analog that is on the surface of the protein in its natural conformation and that does not impair native folding or biological activity of the ribosome-inactivatlng protein. Analogs of bacterial RIPs are also contemplated by the present invention.
The present invention provides an analog of a Type I ribosome-inactivating protein, which analog has a cysteine available for intermolecular disulfide bonding at an amino acid position corresponding to a position not naturally available for intermolecular disulfide bonding in the Type I ribosome-inactivating protein and which cysteine is located at a position in the amino acid sequence of the analog corresponding to position 259 in SEQ ID NO: 1 or at a position in the amino acid sequence in the analog corresponding to a position from position 251 in SEQ ID NO: 1 to the carboxyl terminal position of the analog.
An analog according to the present invention may be an analog of gelonin. In an analog of gelonin according to the present invention, the cysteine may be at a position in the analog from position 244 to the carboxyl terminal position of the analog, more preferably at a position in the analog from position 247 to the carboxyl terminal position of the analog, and most preferably at position 244, at position 247, or at position 248 of the amino acid sequence of the analog. In these analogs, it is preferred that the gelonin cysteine residues at positions 44 and 50 be replaced with non-cysteine residues such as alanine.
An analog according to the present invention may be an analog of barley ribosome-inactivating protein. Preferably, a cysteine in such an analog is at a position in the analog from position 256 to the carboxyl terminal position, and more preferably the cysteine is at a position in the amino acid sequence of the analog from position 260 to the carboxyl terminal position of the analog. Most preferably, in these regions, the cysteine is at position 256, at position 270, or at position 277 of the amino acid sequence of the analog.
An analog according to the present invention may be an analog of momordin IT.
Analogs according to the present invention may have a cysteine in the amino acid sequence of the analog at a position which corresponds to a position within one amino acid of position 259 of SEQ ID NO: 1. Such an analog may be an analog of gelonin, of barley ribosome-inactivating protein, or of momordin II.
The present invention also provides a polynucleotide encoding an analog of a Type I ribosome-inactivating protein, which analog has a cysteine available for intermolecular disulfide bonding at an amino acid position corresponding to a position not naturally available for intermolecular disulfide bonding in the Type I ribosome-inactivating protein, and which cysteine is located at a position in the amino acid sequence of the analog from the position corresponding to position 251 in SEQ ID NO: 1 to the carboxyl terminal position of the analog. The polynucleotide may encode an analog of gelonin, preferably an analog wherein the cysteine is at a position in the amino acid sequence of the analog from position 244 to the carboxyl terminal position of the analog, more preferably wherein the cysteine is at a position in the analog from position 247 to the carboxyl terminal position of the analog, and most preferably the cysteine is at position 244, at position 247 or at position 248 of the amino acid sequence of the analog. It is preferred that a polynucleotide according to the present invention encode a gelonin analog wherein the native gelonin cysteine residues at positions 44 and 50 are replaced with non-cysteine residues, such as alanine.
A polynucleotide according to the present invention may encode an analog of barley ribosome-inactivating protein, preferably an analog wherein the cysteine is at a position in the analog from position 256 to the carboxyl terminal position of the analog, more preferably wherein the cysteine is at a position in the analog from position 260 to the carboxyl terminal position 5of the analog, and most preferably wherein the cysteine is at position 256, at position 270 or at position 277 of the amino acid sequence of the analog.
A polynucleotide according to the present invention may encode an analog of mormordin II.
The present invention provides a vector including a polynucleotide encoding an analog of a Type I ribosome-inactivating protein, which analog has a cysteine available for intermolecular disulfide bonding at a amino acid position corresponding to a position not naturally available for intermolecular disulfide bonding in the Type I ribosome-inactivating protein and which cysteine is located at a position in the amino acid sequence of the analog from the position corresponding to position 251 in SEQ ID NO: 1 to the carboxyl terminal position of the analog.
The present invention further provides a host cell including a DNA vector encoding an analog of a Type I ribosome-inactivating protein, which analog has a cysteine available for intermolecular disulfide bonding at an amino acid position corresponding to a position not naturally available for intermolecular disulfide bonding in the Type I ribosome-inactivating protein and which cysteine is located at a position in the amino acid sequence of the analog from the position corresponding to position 251 in SEQ ID NO: 1 to the carboxyl terminal position of the analog. In such a host cell the vector may encode an analog of gelonin, especially an analog wherein the cysteine is at position 247 of the amino acid sequence of the analog, such as in the host cell deposited as ATCC Accession No. 69009.
A host cell according to the present invention may include a vector encoding barley ribosome-inactivating protein, especially preferred is a host cell containing a BRIP analog wherein the cysteine is at position 277, such as in the host cell deposited on Oct. 2, 1991 with the American Type Culture Collection, 12301 Parklawn Drive, Rockville, Md. 20852 as ATCC Accession No. 68722. Particularly preferred are prokaryotic host cells because such cells may be less sensitive to the action or RIPs as compared to eukaryotic cells.
The present invention also provides an agent toxic to a cell including an analog of a Type I ribosome-inactivating protein linked by a disulfide bond through a cysteine to a molecule which specifically binds to the cell, which cysteine is at an amino acid position in the analog corresponding to a position not naturally available for intermolecular disulfide bonding in the Type I ribosome-inactivating protein and which cysteine is located in the amino acid sequence of the analog from the position corresponding to position 251 in SEQ ID NO: 1 to the carboxyl terminal position of the analog. The agent may include an analog of gelonin, preferably an analog wherein the cysteine is at a position in the analog from position 247 to the carboxyl terminal position of the analog, and more preferably wherein the cysteine is at position 247 or 248 of the amino acid sequence of analog. An agent including an analog wherein the native gelonin cysteine residues at positions 44 and 50 are replaced with non-cysteine residues, such as alanine is preferred.
An agent according to the present invention may include an analog of barley ribosome-inactivating protein, preferably an analog wherein the cysteine is at a position in the analog from position 260 to the carboxyl terminal position of the analog, more preferably wherein the cysteine is at a position in the analog from position 270 to the carboxyl terminal position of the analog, and most preferably wherein the cysteine is at position 256, at position 270 or at position 277 of the amino acid sequence of the analog.
An agent according to the present invention may include an analog of momordin II.
The present invention provides an agent wherein the Type I ribosome-inactivating protein is linked to an antibody, particularly to an H65 antibody or to an antibody fragment, more particularly to an antibody fragment selected from the group consisting of chimeric and human engineered antibody fragments, and most particularly to a Fab antibody fragment, a Fabxe2x80x2 antibody fragment or a F(abxe2x80x2)2 antibody fragment. It is highly preferred that an agent according to the present invention include a chimeric or human engineered antibody fragment selected from the group consisting of a Fab antibody fragment, a Fabxe2x80x2 antibody fragment and a F(abxe2x80x2)2 antibody fragment.
A method according to the present invention for preparing an analog of a Type I ribosome-inactivating protein includes the step of expressing in a suitable host cell a polynucleotide encoding a Type I ribosome-inactivating fusion protein or type I RIP (especially gelonin) having a cysteine available for intermolecular disulfide bonding substituted (e.g., by site-directed mutagenesis of the natural DNA sequence encoding the RIP or by chemical synthesis of a DNA sequence encoding the RIP analog) at an amino acid position corresponding to a position not naturally available for intermolecular disulfide bonding in the Type I ribosome-inactivating protein, which cysteine is located at a position in the amino acid sequence of the analog from the position corresponding to position 251 in SEQ ID NO: 1 to the carboxyl terminal position of the analog.
A product according to the present invention may be a product of a method including the step of expressing in a suitable host cell a polynucleotide encoding a Type I ribosome-inactivating protein having a cysteine available for intermolecular disulfide bonding substituted at an amino acid position corresponding to a position not naturally available for intermolecular disulfide bonding in the Type I ribosome-inactivating protein, which cysteine is located at a position in the amino acid sequence of the analog from the position corresponding to position 251 in SEQ ID NO: 1 to the carboxyl terminal position of the analog.
The present invention provides a method for preparing an agent toxic to a cell including the step of linking an analog of a Type I ribosome-inactivating protein through a cysteine to a molecule which specifically binds to the cell, which analog has the cysteine at an amino acid position corresponding to a position not naturally available for intermolecular disulfide bonding in the Type I ribosome-inactivating protein and which cysteine is located at a position in the amino acid sequence of the analog from the position corresponding to position 251 in SEQ ID NO: 1 to the carboxyl terminal position of the analog.
According to the present invention, a method for treating a disease in which elimination of particular cells is a goal may include the step of administering to a patient having the disease a therapeutically effective amount of an agent toxic to the cells including a type I RIP (especially gelonin fused to or an analog of a Type I ribosome-inactivating protein linked through a cysteine to a molecule which specifically binds to the cell, the analog having the cysteine at an amino acid position corresponding to a position not naturally available for intermolecular disulfide bonding in the Type I ribosome-inactivating protein and the cysteine being located at a position in the amino acid sequence of the analog from the position corresponding to position 251 in SEQ ID NO: 1 to the carboxyl terminal position of the analog.
Useful target cells for immunotoxins of the present invention include, but are not limited to, cells which are pathogenic, such as cancer cells, autoimmune cells, and virally-infected cells. Such pathogenic cells may be targeted by antibodies or other targeting agents of the invention which are joined, either by genetic engineering techniques or by chemical cross-linking, to an RIP. Specifically useful targets include tumor-associated antigens (e.g., on cancer cells), cell differentiation markers (e.g., on autoimmune cells), parasite-specific antigens, bacteria-specific antigens, and virus-specific antigens.
The present invention also provides an analog of a Type I ribosome-inactivating protein, wherein the analog has a cysteine available for intermolecular disulfide bonding located at an amino acid position corresponding to a position not naturally available for intermolecular disulfide bonding in the Type I ribosome-inactivating protein and corresponding to a position on the surface of ricin A-chain in its natural conformation, and wherein the analog retains the ribosome-inactivating activity of the Type I ribosome-inactivating protein.
Such a fusion protein or an analog may be a fusion protein or an analog wherein the Type I ribosome inactivating protein is gelonin, and the analog is preferably an analog of gelonin wherein the cysteine is at position 10 of the amino acid sequence of the analog as encoded in a vector in a host cell deposited with the American Type Culture Collection, 12301 Parklawn Drive, Rockville, Md. 20852 as ATCC Accession No. 69008 on Jun. 9, 1992. Other such gelonin analogs include those wherein the cysteine is at a position 60, 103, 146, 184 or 215 in the amino acid sequence of the gelonin analog. It is preferred that the gelonin cysteine residues at positions 44 and 50 be replaced with non-cysteine residues such as alanine in these analogs.
The present invention further provides an analog of a Type I ribosome-inactivating protein wherein the analog includes only a single cysteine. Such an analog may be an analog of gelonin and is preferably an analog wherein the single cysteine is at position 10, position 44, position 50 or position 247 in the amino acid sequence of the analog, but the cysteine may be located at other positions defined by the invention as well.
The present invention provides a polynucleotide encoding an analog of a Type I ribosome-inactivating protein, wherein the analog has a cysteine available for intermolecular disulfide bonding located at an amino acid position corresponding to a position not naturally available for intermolecular disulfide bonding in the Type I ribosome-inactivating protein and corresponding to a position on the surface of ricin A-chain in its natural conformation, and wherein the analog retains ribosome-inactivating activity of the Type I ribosome-inactivating protein.
According to the present invention, a method for preparing an analog of a Type I ribosome-inactivating protein may include the step of expressing in suitable host cell a polynucleotide encoding a Type I ribosome-inactivating protein having a cysteine available for intermolecular disulfide bonding substituted at an amino acid position corresponding to a position not naturally available for disulfide bonding in the Type I ribosome-inactivating protein, the cysteine is located at a position corresponding to an amino acid position on the surface of ricin A-chain in its natural conformation and which analog retains ribosome-inactivating activity of the Type I ribosome-inactivating protein.
The present invention provides an agent toxic to a cell including an analog of a Type I ribosome-inactivating protein linked by a disulfide bond through a cysteine to a molecule which specifically binds to the cell, wherein the analog has a cysteine available for intermolecular disulfide bonding located at an amino acid position corresponding to a position not naturally available for intermolecular disulfide bonding in the Type I ribosome-inactivating protein and corresponding to a position on the surface of ricin A-chain in its natural conformation, and wherein the analog retains ribosome-inactivating activity of the Type I ribosome-inactivating protein.
A method according to the present invention for preparing an agent toxic to a cell may include the step of linking an analog of a Type I ribosome-inactivating protein through a cysteine to a molecule which specifically binds to the cell, which analog has a cysteine available for intermolecular disulfide bonding located at an amino acid position corresponding to a position not naturally available for intermolecular disulfide bonding in the Type I ribosome-inactivating protein and corresponding to a position on the surface of ricin A-chain in its natural conformation, and which analog retains ribosome-inactivating activity of the Type I ribosome-inactivating protein.
A method according to the present invention for treating a disease in which elimination of particular cells is a goal includes the step of administering to a patient having the disease a therapeutically effective amount of an agent toxic to the cells wherein the agent includes a type I RIP fused to or an analog of a Type I ribosome-inactivating protein linked by a disulfide bond through a cysteine to a molecule which specifically binds to the cell, which analog has a cysteine available for intermolecular disulfide bonding located at an amino acid position corresponding to a position not naturally available for intermolecular disulfide bonding in the Type I ribosome-inactivating protein and corresponding to a position on the surface of ricin A-chain in its natural conformation, and which analog retains ribosome-inactivating activity of the Type I ribosome-inactivating protein.
The RIP analogs of the invention are particularly suited for use as components of cytotoxic therapeutic agents. Cytotoxic agents according to the present invention may be used in vivo to selectively eliminate any cell type to which the RIP component is targeted by the specific binding capacity of the second component. To form cytotoxic agents, RIP analogs may be conjugated to monoclonal antibodies, including chimeric and CDR-grafted antibodies, and antibody domains/fragments (e.g., Fab, Fabxe2x80x2, F(abxe2x80x2)2, single chain antibodies, and Fv or single variable domains). Analogs of RIPs conjugated to monoclonal antibodies genetically engineered to include free cysteine residues are also within the scope of the present invention. Examples of Fabxe2x80x2 and F(abxe2x80x2)2 fragments useful in the present invention are described in co-pending, co-owned U.S. patent application No. 07/714,175, filed Jun. 14, 1991, (abandoned) and in International Publication No. WO 89/00999 published on Feb. 9, 1989, which are incorporated by reference herein.
The RIP analogs of the invention may preferably be conjugated or fused to humanized or human engineered antibodies, such as the he3 antibody described herein. Such humanized antibodies may be constructed from mouse antibody variable domains, such as the mouse antibody H65 (SEQ ID NOS: 123 and 124). Specifically RIP analogs according to the present invention may be conjugated or fused to he3 human-engineered antibody light and heavy chain variable regions (SEQ ID NO: 125 and 126, respectively) or fragments thereof. A cell line producing an intact he3 immunoglobulin was deposited as ATCC Accession No. HB11206 with the American Type Culture Collection, 12301 Parklawn Drive, Rockville, Md. 20852.
RIPs according to the present invention may also be conjugated to targeting agents other than antibodies, for example, lectins which bind to cells having particular surface carbohydrates, hormones, lymphokines, growth factors or other polypeptides which bind specifically to cells having particular receptors. Immunoconjugates including RIPs may be described as immunotoxins. An immunotoxin may also consist of a fusion protein rather than an immunoconjugate.
The present invention provides gene fusions of an antigen-binding portion of an antibody (e.g., an antibody light chain or truncated heavy chain, or a single chain antibody) or any targeting agent listed in the foregoing paragraph, linked to a Type I RIP. Preferably, the antigen-binding portion of an antibody or fragment thereof comprises a single chain antibody, a Fab fragment, or a F(abxe2x80x2)2 fragment. Active antibodies generally have a conserved three-dimensional folding pattern and it is expected that any antibody which maintains that folding pattern will retain binding specificity. Such antibodies are expected to retain target enzymatic activity when incorporated into a fusion protein according to the present invention.
It is sometimes necessary that immunotoxins comprising cytotoxic components, such as RIPs, be attached to targeting agents via cleavable linkers (i.e., disulfides, acid-sensitive linkers, and the like) in order to allow intracellular release of the cytotoxic component. Such intracellular release allows the cytotoxic component to function unhindered by possible negative kinetic or steric effects of the attached antibody. Accordingly, gene fusions of the present invention may comprise a RIP gene fused, via a DNA segment encoding a linker protein as described above, to either the 5xe2x80x2 or the 3xe2x80x2 end of a gene encoding an antibody. If a linker is used, it preferably encodes a polypeptide which contains two cysteine residues participating in a disulfide bond and forming a loop which includes a protease-sensitive amino acid sequence (e.g., a segment of E. coli shiga-like toxin as in SEQ ID NO: 56) or a segment which contains several cathepsin cleavage sites (e.g., a segment of rabbit muscle aldolase as in SEQ ID NO: 57, a segment of human muscle aldolase, or a synthetic peptide including a cathepsin cleavage amino acid sequence). A linker comprising cathepsin cleavage sites as exemplified herein comprises the C-terminal 20 amino acids of RMA. However, that sequence differs by only one amino acid from human muscle aldolase and it is contemplated that muscle aldolase from human or other sources may be used as a linker in the manner described below. The Type I RIP portion of the fused genes preferably encodes gelonin, BRIP or momordin II. Also preferably, the antibody portion of the fused genes comprises sequences encoding one of the chains of an antibody Fab fragment (i.e., kappa or Fd) and the fused gene is co-expressed in a host cell with the other Fab gene, or the antibody portion comprises sequences encoding a single chain antibody.
Alternatively, since fusion proteins of the present invention may be of low (approximately 55 kDa) molecular weight while maintaining full enzymatic activity, such fusions may be constructed without a linker and still possess cytotoxic activity. Such low-molecular weight fusions are not as susceptible to kinetic and steric hinderance as are the larger fusions, such as fusions involving IgG molecules. Therefore, cleavage of the RIP away from the fusion may not be necessary to facilitate activity of the RIP.
The present invention also provides a method for purifying a protein or immunotoxin comprising a ribosome-inactivating protein and a portion of an antibody including the steps of passing a solution containing the protein through an anion exchange column; applying the flow-through to a protein G column; and eluting the protein from the protein G column. The method may further comprise the steps of introducing the flow-through of the anion exchange column into a cation exchange column; exposing the cation exchange column to an eluent effective to elute said protein; and then applying the eluted protein to a protein G column, rather than applying the anion exchange column flow-through directly to a protein G column.
Immunotoxins according to the present invention, including immunoconjugates and fusion proteins (immunofusions), are suited for treatment of diseases where the elimination of a particular cell type is a goal, such as autoimmune disease, cancer, and graft-versus-host disease. The immunotoxins are also suited for use in causing immunosuppression and in treatment of infections by viruses such as the Human Immunodeficiency virus.
Specifically illustrating polynucleotide sequences according to the present invention are the inserts in the plasmid pING3731 in E. coli MC1061 (designated strain G274) and in the plasmid pING3803 in E. coli E104 (designated strain G275), both deposited with the American Type Culture Collection (ATCC), 12301 Parklawn Drive, Rockville, Md., on Oct. 2, 1991, and assigned ATCC Accession Nos. 68721 and 68722, respectively. Additional polynucleotide sequences illustrating the invention are the inserts in the plasmid pING3746 in E. coli ME104 (designated strain G277) and in the plasmid pING3737 in E. coli E104 (designated strain G276), which were both deposited with the ATCC on Jun. 9, 1992, and were respectively assigned Accession Nos. 69008 and 69009. Still other polynucleotide sequences illustrating the invention are the inserts in the plasmid pING3747 in E. coli ME104 (designated strain G278), in the plasmid pING3754 in E. coli E104 (designated strain G279), in the plasmid pING3758 in E. coli E104 (designated strain G280) and in the plasmid pING3759 in E. coli E104 (designated strain G281), which plasmids were all deposited with the ATCC on Oct. 27, 1992 and were assigned ATCC Accession Nos. 69101, 69102, 69103 and 69104, respectively.
As noted above, RIPs may preferably be conjugated or fused to humanized or human-engineered antibodies, such as he3. Thus, the present invention also provides novel proteins comprising an humanized antibody variable domain which is specifically reactive with an human CD5 cell differentiation marker. Specifically, the present invention provides proteins comprising the he3 light and heavy chain variable regions as shown in SEQ ID NOS: 125 or 126, respectively. DNA encoding certain he3 proteins is shown in SEQ ID NOS: 72 and 71.
In a preferred embodiment of the present invention, the protein comprising a humanized antibody variable region is an intact he3 immunoglobulin deposited as ATCC HB 11206.
Also in a preferred embodiment of the invention, the protein comprising a humanized antibody variable region is a Fab or F(abxe2x80x2)2 or Fab fragment.
Proteins according to the present invention may be made by methods taught herein and in co-pending, co-owned U.S. Patent Application No. 07/808,464 (abandoned) incorporated by reference herein; and modified antibody variable domains made by such methods may be used in therapeutic administration to humans either alone or as part of an immunoconjugate as taught in co-owned, co-pending U.S. patent application Ser. No. 07/787,567 (abandoned).
The present invention also provides methods for preparing a modified antibody variable domain useful in preparing immunotoxins and immunofusions by determining the amino acids of a subject antibody variable domain which may be modified without diminishing the native affinity of the domain for antigen while reducing its immunogenicity with respect to a heterologous species. As used herein, the term xe2x80x9csubject antibody variable domainxe2x80x9d refers to the antibody upon which determinations are made. The method includes the following steps: determining the amino acid sequence of a subject light chain and a subject heavy chain of a subject antibody variable domain to be modified; aligning by homology the subject light and heavy chains with a plurality of human light and heavy chain amino acid sequences; identifying the amino acids in the subject light and heavy chain sequences which are least likely to diminish the native affinity of the subject variable domain for antigen while, at the same time, reducing its immunogenicity by selecting each amino acid which is not in an interface region of the subject antibody variable domain and which is not in a complementarity-determining region or in an antigen-binding region of the subject antibody variable domain, but which amino acid is in a position exposed to a solvent containing the antibody; changing each residue identified above which aligns with a highly or a moderately conserved residue in the plurality of human light and heavy chain amino acid sequences if said identified amino acid is different from the amino acid in the plurality.
Another group of sequences, such as those in FIGS. 1A and 1B may be used to determine an alignment from which the skilled artisan may determine appropriate changes to make.
The present invention provides a further method wherein the plurality of human light and heavy chain amino acid sequences is selected from the human consensus sequences in FIGS. 10A and 10B.
In general, human engineering according to the above methods may be used to treat various diseases against which monoclonal antibodies generally may be effective. However, humanized antibodies possess the additional advantage of reducing the immunogenic response in the treated patient.
Additional aspects and applications of the present invention will become apparent to the skilled artisan upon consideration of the detailed description of the invention which follows.